The 1.sub..alpha. -hydroxylated metabolites of vitamin D--most importantly 1.alpha.,25-dihydroxyvitamin D.sub.3 and 1.alpha.,25-dihydroxyvitamin D.sub.2 --are known as highly potent regulators of calcium homeostasis in animals and humans, and more recently their activity in cellular differentiation has also been established. As a consequence, many structural analogs of these metabolites, such as compounds with different side chain structures, different hydroxylation patterns, or different stereochemistry, have been prepared and tested. Important examples of such analogs are 1.alpha.-hydroxyvitamin D.sub.3, 1.alpha.-hydroxyvi tamin D.sub.2, various side chain fluorinated derivatives of 1.alpha.,25-dihydroxyvitamin D.sub.3, and side chain homologated analogs. Several of these known compounds exhibit highly potent activity in vito or in vitro, and possess advantageous activity profiles and thus are in use, or have been proposed for use, in the treatment of a variety of diseases such as renal osteodystrophy, vitamin D-resistant rickets, osteoporosis, psoriasis, and certain malignancies.